1. Optoelectronic Microwave Oscillators
David Yoo
Center for Microwave and Lightwave Engineering
Drexel University
ECE-E641 – Fiber Optics and Optical Communications I
2/20/03
9/19/2018
David Yoo

2. Electronic Oscillators
First developed by L. De Forest in 1912
Noise and stability limitations caused by ohmic and dispersive losses (e.g. in LC circuit)
But these limits can be overcome by combining oscillator with a high Q resonator
9/19/2018
David Yoo

3. Loaded Quality Factor of Resonators
General Definition of Q, the Loaded Quality Factor of a Resonator
9/19/2018
David Yoo

4. Optoelectronic Oscillators
Convert continuous light energy from a laser to RF and microwave signals
Use of fiber as an energy storage device results in signals with extremely low phase noise
Phase noise practically independent of absolute oscillation frequency
9/19/2018
David Yoo

5. OEO Block Diagram Electro-Optic Modulator Optical Fiber Spool
Optical Line Stretcher
Laser
Photodetector
Microwave Output
RF Coupler
RF Bandpass Filter
RF Amplifier
Microwave Spectrum Analyzer
9/19/2018
David Yoo

6. Conditions for Oscillation
Oscillation begins from noise
In order to have self-sustained oscillation :
Open loop gain of system must be greater than unity
An integer number of half-wavelengths must be in the loop
9/19/2018
David Yoo

7. Loop Length and Frequency of Oscillation
The OEO loop can produce a comb of frequencies that satisfy the conditions for oscillation
The Free Spectral Range determines the distance between these frequencies
FSR in loop
Co is speed of light in vacuum
n is index of refraction
Lfiber is physical length of loop
9/19/2018
David Yoo

8. Phase Noise of OEOs Significant noises in an OEO (Yao & Maleki, 1996)
Thermal noise
Shot noise
Intensity noise of laser (RIN)
For high laser optical power, the phase noise of an OEO is limited by the laser’s relative intensity noise
For low laser power, thermal noise tends to dominate
Phase noises as low as -143 dBc/Hz at 10 kHz offset have been achieved for a 10 GHz carrier
9/19/2018
David Yoo

9. OEWaves TIDALWave Fixed frequency (up to 40 GHz)
kHz offset
10 dBm minimum output
10” x 10” x 4”
9/19/2018
David Yoo

10. Recent and Current Work on OEOs
Development of Compact OEOs (1999)
Use of semiconductor lasers and external modulators
Multiloop OEOs (2000)
The 2 fiber loops essentially act as the short and long cavities in a laser to select a single operation mode, and they also permit tunability
Miniaturization of OEOs (currently ongoing)
Replace fiber delay length with fused silica microspherical resonator
Such resonators have Q’s of for optical frequencies
Self Mode-Locking OEO (2002)
9/19/2018
David Yoo

11. Important Points to Remember
Optoelectronic oscillators convert light energy from a laser into RF and microwave signals.
The fiber delays in OEOs are high Q because of the extremely low attenuation rate of fiber.
The phase noise of OEOs tends to be limited by the relative intensity noise of the system’s laser.
9/19/2018
David Yoo